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Properties of Common Inorganic Substances

CSCA Properties of Common Inorganic Substances study guide organized around the publicly available CSCA syllabus. Practice Chemistry questions on aicsca.com.

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Properties of Common Inorganic Substances

1. The "Genetic" Relationship (Transformation Rules)

The key to mastering inorganic chemistry lies in understanding the transformation rules between different categories of substances. This is the foundation for solving Inference Questions.

* **Vertical Series**:

* **Metal Series**: Metal $\rightarrow$ Basic Oxide $\rightarrow$ Base (Alkali) $\rightarrow$ Salt

* **Non-Metal Series**: Non-Metal $\rightarrow$ Acidic Oxide $\rightarrow$ Acid $\rightarrow$ Salt

* **Horizontal Reactions**: Reactions between Acid & Base, or Acidic Oxide & Basic Oxide usually produce **Salt**.

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2. Key Properties Detail

#### 2.1 Elements

* **Metal Activity Series**:

$$K, Ca, Na, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Hg, Ag, Pt, Au$$

* **Displacing Hydrogen**: Metals before $(H)$ can displace hydrogen from **dilute HCl** or **dilute H2SO4**.

* **CSCA Warning**: **Nitric acid ($HNO_3$)** and **Concentrated Sulfuric acid ($H_2SO_4$)** are strong oxidizing agents. They react with metals to produce water and oxides of Nitrogen/Sulfur, **NOT Hydrogen**.

* **Displacing Metals**: A metal can displace any metal following it from its **salt solution** (Exceptions: $K, Ca, Na$ react with water first).

#### 2.2 Oxides

| Category | Definition | Examples | General Equation |

| :--- | :--- | :--- | :--- |

| **Acidic Oxide** | Reacts with base to form salt & water | $CO_2, SO_2, SO_3$ | $CO_2 + 2NaOH \rightarrow Na_2CO_3 + H_2O$ |

| **Basic Oxide** | Reacts with acid to form salt & water | $CaO, CuO, Fe_2O_3$ | $CuO + 2HCl \rightarrow CuCl_2 + H_2O$ |

| **Amphoteric Oxide** | Reacts with both acid and strong base | **$Al_2O_3$** (Important) | $Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O$ |

#### 2.3 Acids, Bases, and Salts

**A. Indicators**

* **Litmus**: Acid $\rightarrow$ Red, Base $\rightarrow$ Blue.

* **Phenolphthalein**: **Acid/Neutral $\rightarrow$ Colorless, Base $\rightarrow$ Red** (Crucial for identifying alkalis).

**B. Conditions for Metathesis (Double Displacement) Reactions**

For a reaction to occur between Acids, Bases, and Salts, one of the following must be produced:

1. **Precipitate** ($\downarrow$)

2. **Gas** ($\uparrow$)

3. **Water**

**C. Colors of Common Precipitates (Must Memorize)**

In CSCA exams, color is often the breakthrough point for inference problems.

* **White**: $AgCl$ (insoluble in acid), $BaSO_4$ (insoluble in acid), $CaCO_3$ (soluble in acid), $Mg(OH)_2$, $Al(OH)_3$.

* **Blue**: $Cu(OH)_2$

* **Red-Brown**: $Fe(OH)_3$

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3. Typical Example Analysis

**Example: Purification**

How to remove a small amount of $CuSO_4$ from a $Na_2SO_4$ solution?

**Analysis**:

1. **Goal**: Remove $Cu^{2+}$, keep $Na^+$ and $SO_4^{2-}$.

2. **Method**: Convert $Cu^{2+}$ into a precipitate using a base.

3. **Reagent**: Add appropriate amount of **$NaOH$ solution**.

* *Wrong choices*: $Ba(OH)_2$ (introduces $Ba^{2+}$ and precipitates sulfate), $KOH$ (introduces impurity $K^+$).

4. **Equation**: $CuSO_4 + 2NaOH \rightarrow Cu(OH)_2\downarrow + Na_2SO_4$.

5. **Operation**: After adding reagent, perform **Filtration**.

4. Common Mistakes

1. **Solubility of Bases**: Insoluble bases (like $Cu(OH)_2$) **do not** change indicator colors and **do not** react with salt solutions.

2. **The Sodium ($Na$) Trap**: When $Na$ is added to $CuSO_4$ solution, it does **not** displace $Cu$. It reacts with water first ($NaOH + H_2$), then the $NaOH$ reacts with $CuSO_4$.

3. **Definition**: $NaHSO_4$ ionizes to give $H^+$, but it is a **Salt**, not an Acid.